Board Game Arena

Please explain what the three buttons at top center do (aboe the map). There is no popup when I hold my mouse on them (I play from a PC with a 2560x1440 monitor).
One is red with the text "Back" on it, the others are blue, one with crossed swords and one with a garbage bin.
They are only visible when I haven't clicked on a piece.

Also, I assume that the diagonal stripes on some areas designate control with the angle of the lines denoting ownership.

Opening the rule book can help you to understand that one is for declaring war and the other for removing piece.
Btw, as all can be undo, why not trying to click on it ?

Thanks.

I did open the rulebook. I haven't read all of it. Unfortunately, the available videos don't help much. I'm struggling a bit with the game - this is the first time I play a Quartermaster game. I guess I will need to read the rules in detail. I find this rulebook a difficult read - I guess that's why the videoes aren't very helpful. So I wanted to try it out with a friend to see if that would help me understand the flow of the game.

So, Undone (Abort) appears after I do something. Good to know. Back seems to be another form of Undone. Clicking it seems to have undone all my movement. I have no idea why I would remove one of my pieces. I guess I'll find out eventually.

Pieces are limited. So you can need to remove a piece somewhere to deploy/recruit the same type elsewhere.